optical rotatory power

https://doi.org/10.1351/goldbook.O04313
angle of optical rotation divided by the optical path length through the medium and by either the mass concentration of the substance giving the specific optical rotatory power α λ θ or by amount concentration, giving the molar optical rotatory power, αm.
Source:
Green Book, 2nd ed., p. 33 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)